Stability and performance of aerobic granular sludge for treatment of textile-dyeing wastewater

In this study, aerobic granular sludge (AGS) was used instead of activated sludge to assess the feasibility of AGS treatment of refractory textile-dyeing wastewater. SVI30 and average sludge size of 31 mL/g and 400 μm in the stable stage, which significantly improved sludge settleability. The experiment was designed with five operation stages, and the removal efficiency of COD and TN achieved 77.2 ± 2.5 % and 64.7 ± 1.7 % in stable stage V. AGS can fully remove pollutants to achieve the highest removal efficiency, and shortens the hydraulic retention time and air flow rate, thus saves energy and maintains stability. The specific oxygen uptake rate, nitrification rate, and denitrification rate of sludge in the system had the same change trend and peaked in the AGS maturity stage, which was 39.8 ± 0.6 mg O2/g vss·h, 4.4 ± 0.2 mg NH4+–N/g vss·h, 9.0 ± 0.5 mg NO3−–N/g vss·h, respectively. The genera Candidatus_Competibacter (12.1–18.9 %) and unclassified_f__Comamonadaceae (15.5–22.4 %) were the most abundant denitrifying bacteria after granulation. The toxic tolerant bacteria norank_o__SBR1031, norank_f__A4b, Immundisolibacter, norank_o__Ardenticatenales, and norank_f__Caulobacteraceae were enriched in granules, which enhanced the sludge resistance. This work provides insights for AGS in the face of refractory textile-dyeing wastewater, which helps to enhance the removal efficiency of nutrients and sludge resistance.